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Lung and liver problems caused the death of the Smithsonian National Zoo’s 6-day-old panda cub, zoo officials announced on Oct. 11 in a press conference.

A necropsy revealed the cub’s liver failed to receive enough oxygen due to its underdeveloped lungs, NBC reported. Although Suzan Murray, the zoo’s head veterinarian, had initially described the cub, thought to be a female, to NBC as “just beautiful” after its birth on Sept. 16, it shockingly died less than one week later.

A preliminary autopsy after its death on Sept. 23 found she had liver abnormalities, including discoloration, and fluid in her abdomen. “The liver — by palpation, by touching — felt a little bit hard in places, and it also appeared abnormal,” Murray told NBC. “Typically, livers have a very uniform color.” Murray explained that the lack of oxygen in the cub’s liver, spurred by its underdeveloped lungs, had led to the death of liver cells.

The cub falls into the 20% of female panda babies born in captivity that die before reaching their first birthday, according to NBC. Fortunately, Mei Xiang, the cub’s mother, has slowly returned to normal behavior, showing that almost a month later, she is moving on from her loss. Immediately after her baby’s death, she seemed to have to have a hard time accepting she lost her young.

Keepers told NBC they saw her cradling a toy, a nurturing gesture that expressed her “natural mothering instinct.” But now Mei Xiang is eating about 80% to 85% of her normal diet — whereas new mothers often refrain from eating and drinking for the first week their cubs are alive to care for them. Zoo officials told USA Today that Mei Xiang is consuming “almost all of her bamboo and all of her leaf eater biscuits and produce.”

The mother doesn’t spend much time inside the panda house anymore, either, where she had constructed a nest for her baby. Keepers started to remove the nest on Oct. 10, NBC reported. The cub was the second born to Mei Xiang and partner Tian Tian and was considered something of a miracle after five failed pregnancies. Keepers were unsure if Mei Xiang was still fertile.

“We are happy to report that Mei is almost completely back to her old self! Her hormones have returned to normal levels, as has her behavior,” zoo officials told USA Today. “Mei is choosing to go outside in the mornings. In the afternoons she can usually be found napping on her indoor rock work.”

Mei Xiang and her mate Tian Tian are on loan from China through 2015, but one of them may be replaced if breeding issues arise. The zoo will decide what to do with the couple this fall, USA Today reported.